High power diode-pumped lasers have been a subject of intense research recently. Powers in the range of several 100 Watts have been demonstrated from such laser systems. However, with respect to fundamental mode operation (TEM00-mode), such diode-pumped laser sources have shown only a few tens of Watts of output power even in various approaches to the matter. These TEM00, high power diode-pumped laser sources are typically based on the laser mediums Nd:YAG, Nd:Vanadate, Nd:YLF or Yb:YAG. However, in the case of generating TEM00 modelocked output (picosecond or femtosecond pulses) or TEM00 frequency doubled output (green at a wavelength of 532 nm from diode-pumped Nd:Vanadate, for example), even in relatively complicated setups lower powers of the order of 10 Watts or less have been produced. Among the challenges are: keeping the overall setup simple and compact; in modelocked systems: keeping the pulse width as short as possible for subsequent nonlinear optical applications (<10 ps for Nd:Vanadate, for example), in modelocked systems using semiconductor saturable absorbers: finding a design which puts the laser safely into stable modelocking sufficiently far above the modelocked-Q-switching threshold, in intracavity frequency converted laser systems: avoiding the “green problem” or similar output instabilities.
It has long been thought that intracavity optical frequency doubling is subject to the “green problem”, which results in unstable fluctuations of the frequency-converted output from the laser. Recently some setups have been disclosed which overcame this problem. This invention shows another method to avoid the green problem.
Modelocking of solid state lasers has been achieved with semiconductor saturable absorbers. However, the dynamics of the modelocking calls for high gain saturation, which can be achieved with the schemes described here. The higher the gain saturation, the lower the pulse energy density on the semiconductor saturable absorber can be reducing the degradation rate of the semiconductor saturable absorber. High gain saturation is usually obtained by achieving high pump intensity, which is however limited by the fracture limit of laser materials. Therefore, pump powers in these types of lasers have typically been limited to 10–20 W pump power per spot in state-of-the-art Nd:Vanadate lasers, or multiple pump spots have been used, adding complexity to the system. Furthermore, thermal lensing limits the maximum pump power per spot.